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The ability of light to change the properties of light‐responsive polymers opens avenues for targeted release of cargo with a high degree of spatial and temporal control. Recently, we established photoacid polymers as light‐switchable macromolecular amphiphiles. In these systems, light‐induced excited‐state proton transfer (ESPT) causes changes in amphilicity. However, as the intermolecular process itself critically depends on the local environment of the photoacid unit within the polymer, the overall amphiphilicity directly influences ESPT. Thus, understanding the impact of the local environment on the photophysics of photoacidic side chains is key to material design. In this contribution we address both thermodynamic and kinetic aspects of ESPT in oxazoline‐based amphiphilic polymers with pyrenol‐based photoacid side chains. We will compare the effect of polymer design, i. e. statistical and block arrangements, i. e. in poly[(2‐ethyl‐2‐oxazoline)‐co‐(1‐(6/8‐hydroxyperene)sulphonylaziridine)] and poly(2‐ethyl‐2‐oxazoline)‐block‐poly[(2‐ethyl‐2‐oxazoline)‐co‐(2‐(3‐(6‐hydroxypyrene)sulphonamide)propyl‐2‐oxazoline), on the intermolecular proton transfer reaction by combining steady‐state and time‐resolved absorption and emission spectroscopy. ESPT appears more prominent in the statistical copolymer compared to a block copolymer with overall similar pyrenol loading. We hypothesize that the difference is due to different local chain arrangements adopted by the polymers in the two cases. [ABSTRACT FROM AUTHOR]

Photoacids and bases allow remote control over pH in reaction solutions, which is of fundamental importance to an array of applications. Herein, we determine the wavelength‐by‐wavelength resolved photoreactivity of triarylsulfonium hexafluorophosphate salts as a representative photoacid generator and p‐(benzoyl)benzyl triethylammonium tetraphenylborate as a photobase generator, constructing a wavelength‐resolved photochemical action plot for each of the compounds. We monitor the pH change of the solution on‐line within the cavity of the laser vial and demonstrate a marked mismatch between the absorption spectrum of the photoacid and base with the photochemical action plot, unveiling reactivity at very low absorptivities. Our findings are of critical importance for the use of photoacids and bases, unambiguously demonstrating that absorption is no guide to chemical reactivity with critical consequences for the wavelength employed in applications of photoacids and bases. [ABSTRACT FROM AUTHOR]

Metastable‐state merocyanine photoacids (MCHs) have been widely applied to various chemical, material and biomedical areas to drive or control chemical processes with light. In this work, stoichiometry and association constants have been determined for inclusion complexes of a photoacid MCH1 ((E)‐3‐(2‐(2‐hydroxystyryl)‐3,3‐dimethyl‐3H‐indol‐1‐ium‐1‐yl)propane‐1‐sulfonate) with β‐cyclodextrin (β‐CD), 2‐hydroxypropyl‐β‐CD (HP‐β‐CD), γ‐CD and HP‐γ‐CD by means of UV‐Vis absorption spectroscopic titrations. The inclusion complexes were studied to enhance acidity and chemical stability. Kinetic study showed that CDs stabilized the acidic metastable state and slowed its thermal relaxation. The acidity of the ground and metastable state (pKaGS and pKaMS) increased upon addition of CDs. The pKaMS of [MCH1 ⋅ (γ‐CD)2] is as low as 0.92 in comparison with 2.24 for MCH1, which is close to the lowest pKaMS values (1.20 and 1.03) reported previously, in which case the MCH1 was structurally modified with alkylammonium side chains. Addition of CDs also significantly enhanced the chemical stability of MCH1 against hydrolysis, which is one of the major concerns for the application of MCHs. In particular, the addition of HP‐β‐CD increased the half‐life of MCH1 in aqueous solution more than four‐fold. Moreover, the quantum chemical calculations confirmed the stoichiometry and analyzed the binding sites and hydrogen bonds of the inclusion complexes. [ABSTRACT FROM AUTHOR]

This article epitomizes the design and synthesis of a potential bioactive Semicarbazone Schiff base (E)‐2‐(4‐(diethylamino)‐2‐hydroxybenzylidene)hydrazine‐1‐carboxamide (DHHC) and its water assisted photoinduced tautomerization. DHHC is feebly emissive in non‐polar solvents but the fluorescence intensity intensifies (at 406 nm) in alcohols possibly due to intermolecular H‐bonding. However, in protic polar water, the scenario is markedly different, the fluorescence intensity decreases a bit as compared to alcohols and the emission maxima shifted from 406 nm to 430 nm probably due to solvent (water) assisted excited state proton transfer reaction (ESPT). In contrast to the reported excited state intramolecular proton transfer reaction (ESIPT) in various compounds, DHHC on photoexcitation loses a proton from its phenolic ‐OH group to the water molecule, which insists a subsequent proton transfer from the hydronium ion to the imine nitrogen of DHHC resulting 24 nm red‐shifted fluorescence emission from the tautomeric species of DHHC, in aqueous media. The mechanism of ESPT reaction is explained theoretically through the reaction kinetics of the DHHC‐water complex (in ratio 1 : 3) in an explicit CPCM solvent model. The illustration of the findings may open up enormous possibilities for Semicarbazone Schiff bases to be used as a probe for water sensing inside biomacromolecules like proteins and enzymes. [ABSTRACT FROM AUTHOR]

The possibilities and problems to predict excited‐state acidities and basicities in water with electronic structure calculations combined with a continuum solvation model are investigated for a test set of photoacids and photobases. Different error sources, like errors in the ground‐state pKa values, the excitation energies in solution for the neutral and (de‐)protonated species, basis set effects, and contributions beyond implicit solvation are investigated and their contributions to the total error in pKa∗ are discussed. Density functional theory in combination with the conductor like screening model for real solvents and an empirical linear Gibbs free energy relationship are used to predict the ground‐state pKa values. For the test set, this approach gives more accurate pKa values for the acids than for the bases. Time‐dependent density‐functional theory (TD‐DFT) and second‐order wave function methods in combination with the conductor like screening model are applied to compute excitation energies in water. Some TD‐DFT functionals fail for several species to predict correctly the order of the lowest excitations. Where experimental data for absorption maxima in water is available, the implicit solvation model leads with the applied electronic structure methods in most cases for the excitation energies in water to an overestimation for the protonated and to an underestimation for the deprotonated species. The magnitude and sign of the errors depend on the hydrogen bond donating and accepting ability of the solute. We find that for aqueous solution this results generally in an underestimation in the pKa changes from the ground to the excited state for photoacids and an overestimation for photobases. [ABSTRACT FROM AUTHOR]

Light is a common source of energy in sustainable technologies for photocurrent generation. To date, in such light‐harvesting applications, the excited electrons generate the photocurrent. Here, we introduce a new mechanism for photocurrent generation that is based on excited state proton transfer (ESPT) of photoacids and photobases that can donate or accept a proton, respectively, but only after excitation. We show that the formed ions following ESPT can either serve as electron donors or acceptors with the electrodes, or modify the kinetics of mass transport across the diffuse layer, both resulting in photocurrent generation. We further show that control of the current polarity is obtained by switching the irradiation between the photoacid and the photobase. Our study represents a new approach in photoelectrochemistry by introducing ESPT processes, which can be further utilized in light‐responsive energy production or energy storage. [ABSTRACT FROM AUTHOR]

Photoacids show a strong increase in acidity in the first electronic excited state, enabling real‐time studies of proton transfer in acid‐base reactions, proton transport in energy storage devices and biomolecular sensor protein systems. Several explanations have been proposed for what determines photoacidity, ranging from variations in solvation free energy to changes in electronic structure occurring along the four stages of the Förster cycle. Here we use picosecond nitrogen K‐edge spectroscopy to monitor the electronic structure changes of the proton donating group in a protonated aromatic amine photoacid in solution upon photoexcitation and subsequent proton transfer dynamics. Probing core‐to‐valence transitions locally at the amine functional group and with orbital specificity, we clearly reveal pronounced electronic structure, dipole moment and energetic changes on the conjugate photobase side. This result paves the way for a detailed electronic structural characterization of the photoacidity phenomenon. [ABSTRACT FROM AUTHOR]

Appropriately substituted 1,1′-bi-2-naphthols (BINOLs) are demonstrated as effective photoacid catalysts for promoting the acetalization of enol ethers with alcohols under irradiation with visible light. The reactions proceed efficiently with a wide range of substrates under mild, near neutral conditions. [ABSTRACT FROM AUTHOR]

Nature demonstrates many examples of response and adaptation to external stimuli. Here, this study focuses on self-propulsion (motion) while presenting several self-propelling droplet systems responsive to pH gradients. Light is used as the gating source to gain reversibility, avoid the formation of chemical wastes, and control the self-propulsion remotely. To achieve light-stimuli ultrafast response, photoacids and photobases are used, capable of donating or capturing a proton, respectively, in their excited state. The movement and directionality of the droplet's self-propulsion are controlled by introducing the photoacid/base either in bulk solution, on the surface of the droplet, or inside the droplet. It is shown that proton transfer between the photoacid/base and the droplet results in a rapid change in the droplet's surface tension, which induces the self-propulsion movement. The high versatility of the systems together with a record-breaking ultrafast response to light makes them highly attractive for the design of various controlled cargo-carrier systems. [ABSTRACT FROM AUTHOR]

Light is a convenient source of energy and the heart of light‐harvesting natural systems and devices. Here, we show light‐modulation of both the chemical nature and ionic charge carrier concentration within a protein‐based biopolymer that was covalently functionalized with photoacids or photobases. We explore the capability of the biopolymer‐tethered photoacids and photobases to undergo excited‐state proton transfer and capture, respectively. Electrical measurements show that both the photoacid‐ and photobase‐functionalized biopolymers exhibit an impressive light‐modulated increase in ionic conductivity. Whereas cationic protons are the charge carriers for the photoacid‐functionalized biopolymer, water‐derived anionic hydroxides are the suggested charge carriers for the photobase‐functionalized biopolymer. Our work introduces a versatile toolbox to photomodulate both protons and hydroxides as charge carriers in polymers, which can be of interest for a variety of applications. [ABSTRACT FROM AUTHOR]

Fluorescent dyes are common tools for tracking biological membranes. In this work, we introduce a new ratiometric fluorescent probe for membranes based on a surface‐sensitive photoacid. As all other probes, it lights up within membranes, and furthermore, it has different ratios of fluorescent peaks for different membranes. The main unique feature of the probe is its ability to sense events taking place in the membrane far away from its actual location. This is due to the photoacidity of the probe, and the associated kinetics of its excited‐state proton release and capture that are highly sensitive to the lateral proton diffusion on the surface of the membrane. We show here that minor disruptions to the membrane integrity, induced by the Triton X‐100 surfactant at low concentration (surfactant:lipid ratio of 0.02), can be sensed by our probe using steady‐state fluorescence, while other probes are invisible to them. Time‐resolved fluorescence reveals that the surfactant insertion affects the lateral proton diffusion and accordingly the measured proton recombination of the photoacid. [ABSTRACT FROM AUTHOR]

Photoacids are molecules that become more acidic upon absorption of light. They are widely utilized in a variety of fields, such as organic synthesis, molecular switching agents, and photodynamic therapy. Currently, the activity of most photoacids is induced by UV light, which limits their applications by the synthetic community. In this -Synpacts article, we highlight our recent development of visible-light--induced photoacids and their application in glycosylation reactions. 1 Introduction 2 Visible-Light-Induced Photoacids 3 Synthesis of 2-Deoxyglycosides by Visible-Light-Induced Photoacid Catalysis 4 Conclusion [ABSTRACT FROM AUTHOR]

The self‐assembly of low molecular weight gelators in water usually produces homogeneous hydrogels. However, homogeneous gels are not always desired. Using a photoacid generator, it is shown how to form gels with a transient gradient in stiffness, proved using cavitation and bulk rheology. Small‐angle neutron scattering is used to show that the gels formed by photoacid are the result of the same structures as when using a conventional pH trigger. Patterned gels can also be formed, again with transient differences in stiffness. [ABSTRACT FROM AUTHOR]

The synthesis of a photoresponsive amphiphilic diblock quarterpolymer containing 5‐vinyl‐1‐naphthol (VN) as a photostable photoacidic comonomer is presented. The preparation is realized via a sequential reversible addition fragmentation chain transfer (RAFT) polymerization starting from a nona(ethylene glycol) methyl ether methacrylate (MEO9MA/"O") hydrophilic block, which is then used as a macro‐RAFT agent in the terpolymerization of styrene (S), 2‐vinylpyridine (2VP), and TBS‐protected VN (tVN). The terpolymerization proceeds in a controlled fashion and two diblock quarterpolymers, P(Om)‐b‐P(Sx‐co‐2VPy‐co‐VNz), with varying functional comonomer compositions are prepared. These diblock quarterpolymers form spherical core‐corona micelles in aqueous media according to dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo‐TEM). Upon irradiation, the photoacids within the micellar core experience a drastic increase in acidity causing a proton transfer from the photoacid to neighboring 2VP units. As a result, the hydrophilic/hydrophobic balance of the entire assembly is shifted, and the encapsulated cargo is released. [ABSTRACT FROM AUTHOR]

3-Hydroxynaphtho[1,2-b]quinolizinium was synthesized by cyclodehydration route and its optical properties in different media were investigated. The absorption and emission spectra of this compound depend on the pH of the solution. Thus, at higher pH values the deprotonation yields a merocyanine-type dye that exhibits significantly red-shifted absorption bands and causes a dual emisson, i.e., a combination of emission bands of the hydroxyquinolizinium and its deprotonated form. Whereas this compound is a weak acid in the ground state (pKa = 7.9), it has a strongly increased acidity in the excited state (pKa* = 0.4). As a result, the blue-shifted fluorescence of the hydroxyquinolizinium becomes dominant only under strongly acidic conditions. In addition, it is shown that 3-hydroxynaphtho[1,2-b]quinolizinium binds to cucurbit[7]uril (CB[7]) with moderate affinity (Kb = 1.8 × 104 M−1, pH 5) and that the pKa and pKa* values of this ligand increase by about two to three orders of magnitude, respectively, when bound to CB[7].

The combination of styryl dye properties with the acidity and strong photoacidity of the 2,2′‐[(1′′‐hydroxy‐4′′‐methyl‐(E)‐2′′,6′′‐phenylene)]‐bisquinolizinium enables the detection of DNA by distinct absorption and emission color changes and the fluorimetric detection of DNA in cells with epifluorescence and confocal fluorescence microscopy. [ABSTRACT FROM AUTHOR]

Recently, metastable‐state photoacids have been widely used to control proton transfer in numerous chemical and biological processes as well as applications with visible light. Generally, substituents have a great influence on the photochemical properties of molecules, which will further affect their applications. Yet, the effects of substituents on metastable‐state photoacids have not been studied systematically. In this work, 16 metastable‐state photoacid derivatives were designed and synthesized on the basis of substituents having a large range of σ–π electron–donor–acceptor capabilities. The effects of substituents on the color display [or maximum absorption band(s)], solubility, pKa values, dark/photoacidity, photosensitivity, and relaxation kinetic(s) were investigated in detail. This study will be helpful for the targeted design and synthesis of promising photoacids and the application of their photocontrolled proton‐release processes in functional materials/devices. Controlled proton release: The effects of substituents on the color display, solubility, pKa values, dark/photoacidity, photosensitivity, and relaxation kinetics of metastable‐state photoacid derivatives are investigated. This study will help with the targeted design and synthesis of promising photoacids and application of their photocontrolled proton‐release processes in functional materials/devices. MEHs=merocyanines, SPs=spiropyrans. [ABSTRACT FROM AUTHOR]

[Display omitted] • We report the photophysical properties of 7-hydroxy coumarin-3-carboxylic acid (7–HCCA). • Presence of neutral, anionic and di-anionic forms of 7–HCCA was observed in cationic micelles. • Due to electrostatic interaction quantum yield of 7-HCCA decreases in cationic micelles. • The photophysical properties of 7-HCCA modulated with the variation of chain length and head group of the surfactants. • Effect of pH of the media on the photophysical properties of 7-HCCA in micellar systems were reported. 7-Hydroxy coumarin-3-carboxylic acid (7-HCCA) is a photoacid that exists in three distinct forms: neutral, anionic and di-anionic. It falls under the category of hydroxy aromatic and carboxy aromatic molecules. This molecule exhibits strong fluorescence and is commonly employed in the detection of hydroxyl radicals. In our study, we utilised absorption and fluorescence spectroscopy to investigate the photophysical behaviour of 7-HCCA in different micellar systems. Through our experiments, we observed that as we varied the pH within the ranges of 2–3, 4–6, 7–10, the three aforementioned forms of 7-HCCA are emerged. Specifically, in cationic surfactants, the dye displayed an equilibrium between two forms of the 7-HCCA in the ground state at any pH. Furthermore, our steady-state excitation studies also proved the presence of an equilibrium between two forms of the 7-HCCA in all cationic systems. By examining the steady-state emission spectra, we also observed the presence of two distinct species in the excited state. When cationic surfactants were introduced, we observed a decrease in the fluorescence intensity and quantum yield compared to that observed in the water medium. It was evident that the photophysical properties of 7-HCCA were modulated with variations of the chain length and head group of the surfactants. In summary, our investigation shed light on the photophysical characteristics of 7-HCCA in different micellar systems with varying the pH. By employing the absorption and fluorescence spectroscopy, we successfully identified the coexistence of multiple forms of 7-HCCA and observed how the cationic surfactants influenced its fluorescence emission properties, ultimately contributing to a deeper understanding of its behaviour in these systems. [ABSTRACT FROM AUTHOR]

Photophysical properties of some 1-naphthol and 2-naphthol sulfonate derivatives and their efficiency as singlet oxygen photosensitizers in aqueous media are reported. The fluorescence emission is mainly from the deprotonated form (conjugate base) and their maxima cover the range of 433–529 nm. The fluorescence decay of these derivatives was found to be fitted with bi-exponential function with χ 2 of about 1.0 ± 0.1 in all cases. Rate constants for oxygen quenching of the excited singlet states of these compounds in H 2 O are found to be (1.2 ± 0.2) × 10 10  M −1  s −1 for the neutral form and much lower for the quenching of their conjugate bases. p K a   values were found to be in the range 7.4–9.5 while p K a * are close to zero and about 3.3 for 2-naphthol and 2-naphthol-6-sulfonate using Förster equation and in the range of 1.4–3.0 using the fluorescence titration method obtained from the relative integrated fluorescence intensity. Singlet oxygen quantum yields photosensitized by these photoacids were reported in D 2 O and found to be in the range 0.13–0.35 for the sulfonated derivatives. [ABSTRACT FROM AUTHOR]

Abstract: The direct, photoacid‐catalyzed synthesis of 2‐deoxyglycosides from glycals is reported. A series of phenol‐conjugated acridinium‐based organic photoacids were rationally designed, synthesized, and studied alongside the commercially available phenolic catalyst eosin Y. In the presence of such a photoacid catalyst and light, synthetic glycals were activated and coupled with a range of alcohols to afford 2‐deoxyglycosides in good yields and with excellent α‐selectivity. [ABSTRACT FROM AUTHOR]

Photochemical reaction of trans -2,6-diaryl-4 H -spiro[cyclohexane-1,2′-indene]-1′,3′,4-triones gives rise to the formation of the ylidenephthalide derivatives as previously observed for 2,2-disubstituted 1,3-indandiones. In contrast, the respective cis -isomers afford different products originating from the unprecedented reversible cyclohexanone cycle breaking (photo-induced retro-Michael reaction). The difference between the reaction pathways does not depend on the irradiation wavelengths or the light source power and is observed both in solution and solid state. [ABSTRACT FROM AUTHOR]

Photoinduced transformations of (E) -2-(2-hydroxystyryl)quinazolinone-linked benzo[15(18)]crown-5(6) ethers in solutions have been studied by using UV–vis absorption and NMR spectroscopy. These crown ethers were found to have dual emission at 520 and 650 nm, associated with proton-transfer tautomer emission (ESIPT-luminescence) as a rare case of excited-state proton-transfer reaction in the non-pseudocyclic chromophoric systems. It was established also, that the organic bases affect the luminescence intensity of solutions of these compounds in the 550–650-nm wavelength range. An X-ray crystallography analysis of molecular structures of crown ethers and their complexes in crystals has been carried out. The fact of reversible photo/thermal E - Z isomerization in DMF and Et 3 N for these macroheterocyclic compounds has been confirmed. An opportunity to control the photochemical isomerization rate of quinazolinone 2-(hydroxyphenyl)ethenyl derivatives by changing pH of the medium has been demonstrated. [ABSTRACT FROM AUTHOR]

Enhancing solar energy conversion efficiency is very important for developing renewable energy, protecting the environment, and producing agricultural products. Efficient enhancement of photophosphorylation is demonstrated by coupling artificial photoacid generators (PAGs) with chloroplasts. The encapsulation of small molecular long-lived PAGs in the thylakoid lumen is improved greatly by ultrasonication. Under visible-light irradiation, a fast intramolecular photoreaction of the PAG occurs and produces many protons, remarkably enhancing the proton gradient in situ. Consequently, compared to pure chloroplasts, the assembled natural-artificial hybrid demonstrates approximately 3.9 times greater adenosine triphosphate (ATP) production. This work will provide new opportunities for constructing enhanced solar energy conversion systems. [ABSTRACT FROM AUTHOR]

The urgent implementation of emissions control measures is inhibited in part by the expense of carbon capture technology. A large part of the cost of amine based approaches is in the heat regeneration of the absorbent. An alternative way to do this could be through use of abundant solar energy. In a new approach, direct chemical action on the absorbed CO 2 was achieved by use of a reversible photoacid. Irradiation of the CO 2 loaded solution resulted in CO 2 removal by action of light. [ABSTRACT FROM AUTHOR]

Steady-state and time-resolved optical spectroscopy techniques were employed to study the photophysics and photochemistry of 4- (4HC) and 3-hydroxycoumarin (3HC). We found that the p K a of 4HC in aqueous solutions is about 7.5 and the p K a * is only 4.5. We also found that the nonradiative rate of 4-hydroxycoumarin is high and the excited state proton transfer (ESPT) rate to water is rather slow and so an ESPT process is not observed. Quantum mechanical calculations confirm that the ESPT rate should be slow and the intersystem crossing rate S 1 → T is large. An ESPT process was also not observed for 3HC, but it might still take place and not being observed as the fluorescence quantum yield of the anion is two orders of magnitude smaller than that of the protonated form. The nonradiative decay of protonated 3HC is explained with an H-atom abstraction mechanism, leading to the formation of a radical species. [ABSTRACT FROM AUTHOR]

Neutral eosin Y‐derived photoexcited states have been found to serve as photoacids and direct hydrogen atom transfer (HAT) catalysts in the activation of glycals and C−H bonds, respectively. These studies pave the way for further use of eosin Y in photochemical synthesis. New sides of eosin Y: Neutral eosin Y‐derived photoexcited states have been found to serve as photoacids and direct hydrogen atom transfer (HAT) catalysts in the activation of glycals and C−H bonds, respectively. These studies pave the way for further use of eosin Y in photochemical synthesis. [ABSTRACT FROM AUTHOR]

We studied the excited-state intramolecular proton transfer (ESIPT) of two derivatives of hydroxybenzo[ h ]quinoline (10-HBQ). We used time-resolved and steady-state techniques for this purpose. These two compounds are water soluble and can be excited by visible light, thus they have a potential use in in vitro and in vivo imaging applications. We found that the ESIPT rate of ortho-indolium-10-hydroxybenzo[ h ]quinoline is greater than 10 13 s −1 , whereas for ortho-picolinium-10-hydroxybenzo[ h ]quinoline the rate constant is rather low ( k PT = 7 × 10 12 s −1 , τ PT = 140 ± 20 fs). We also found a kinetic isotope effect of 1.5 ± 0.2 for ortho-picolinium-10-hydroxybenzo[ h ]quinoline. We observe in both compounds, a slower time component of 300 ± 50 fs with low amplitude of 0.05 ± 0.02 for the enol form decay. This slower component is also observed in the fluorescence-signal rise of the keto form, but with a higher amplitude of 0.2 ± 0.04. The fluorescence-signal rise of the keto forms of both compounds shows a third long-time component of several picoseconds. This time component in ortho-indolium-10-hydroxybenzo[ h ]quinoline is solvent-dependent and is assigned to solvation dynamics in protic solvents. We explain the relatively slow ESIPT rate of ortho-picolinium-10-hydroxybenzo[ h ]quinoline by the smaller enol-keto energy gap of this compound. [ABSTRACT FROM AUTHOR]

We report a straightforward method for creating large-area, microscale resolution patterns of functional amines on self-assembled monolayers by the photoinduced local acidification of a flat elastomeric stamp enriched with photoacid. The limited diffusivity of the photoactivated merocyanine acid in poly(dimethylsiloxane) (PDMS) enabled to confine efficient deprotection of N - tert -butyloxycarbonyl amino group ( N -Boc) to line widths below 10 μm. The experimental setup is very simple and is built around the conventional HD-DVD optical pickup. The method allows cost-efficient, maskless, large-area chemical patterning while avoiding potentially cytotoxic photochemical reaction products. The activation of the embedded photoacid occurs within the stamp upon illumination with the laser beam and the process is fully reversible. Preliminary positive results highlight the possibility of repeatable use of the same stamp for the creation of different patterns.

Sebastian Eckert et al. show in their Research Article (e202200709) how time-resolved nitrogen K-edge spectroscopy along the Förster cycle of a photoacid provides key insight into the electronic structural factors responsible for the photoacidity phenomenon. Keywords: Aromaticity; Electronic Structure; Orbital Interactions; Photoacids; Time-Resolved Soft x-Ray Spectroscopy EN Aromaticity Electronic Structure Orbital Interactions Photoacids Time-Resolved Soft x-Ray Spectroscopy 1 1 1 06/29/22 20220704 NES 220704 B Photoacids b have been understood, since the pioneering work of Theodor Förster more than seven decades ago, to show a pronounced increase in acidity when electronically excited, but the underlying microscopic mechanisms have remained elusive. Aromaticity, Electronic Structure, Orbital Interactions, Photoacids, Time-Resolved Soft x-Ray Spectroscopy. [Extracted from the article]

Highlights: [•] Two very strong photoacids QCy7, , and QCy9, , are studied in three protic solvents, water, MeOH and EtOH. [•] Weak photoacids do not transfer a proton to alcohols within the excited state lifetime, whereas strong photoacids do. [•] In QCy7 the ESPT rate constant, k PT in water, methanol and ethanol is 1.2×1012, 8×1011 and 7×1011 respectively. [•] The ESPT rate of QCy9 in these solvents is the same, k PT ∼1013 s−1. [•] Non-adiabatic and adiabatic PT theories explain the k PT solvent dependence of weak and very strong photoacids respectively. [ABSTRACT FROM AUTHOR]

A new photoacid that reversibly changes from a weak to a strong acid under visible light was designed and synthesized. Irradiation generated a metastable state with high CH acidity due to high stability of a trifluoromethyl-phenyl-tricyano-furan (CF3PhTCF) carbanion. This long-lived metastable state allows a large proton concentration to be reversibly produced with moderate light intensity. Reversible pH change of about one unit was demonstrated by using a 0.1 m M solution of the photoacid in 95 % ethanol. The quantum yield was calculated to be as high as 0.24. Kinetics of the reverse process can be fitted well to a second-order-rate equation with k=9.78×102 M−1 s−1. Response to visible light, high quantum yield, good reversibility, large photoinduced proton concentration under moderate light intensity, and good compatibility with organic media make this photoacid a promising material for macroscopic control of proton-transfer processes in organic systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Firefly luciferin presents an efficient fluorescence quenching. [•] This is caused by excited state protonation of the benzothiazole nitrogen heteroatom. [•] This protonation leads to intersystem crossing with triplet states. [•] These triplet states are dark or nearly dark excited states. [Copyright &y& Elsevier]

Four cyano groups have been substituted on the aromatic ring of p-hydroquinone (2,3,5,6-tetracyanohydroquinone) in order to study the enhanced photoacidity of this molecule. The acid-base equilibria have been studied using absorption (for ground state pK) and fluorescence (excited state pK) spectra. Three distinct species (neutral, anionic and dianionic forms) were observed in the ground state and only two species (anionic and dianionic forms) were found in the excited state when studied at different pH/H in water. Absorption and emission characteristics were studied in various organic solvents, including protic and aprotic solvents. Deprotonation was also investigated using binary mixtures. It has been revealed that absorption and emission spectra are considerably changed with change in media. Proton transfer to the solvent has been observed in various solvents. [ABSTRACT FROM AUTHOR]

The article focuses on the study which observes the level crossing (LC) that occurs in two lowest electronic excited singlet states of 1-naphthol (1N) assisted with ultrafast solvent. The study is investigated by ultrafast fluorescence anisotropy, polarization-resolved femtosecond fluorescence, and time-dependent density functional theory (TDDFT). Results show that the electronic excited-state dynamics of 1N undergoes nondiabatic transitions with level inversion.

Data on the development of new functional compounds and materials based on the study of the reactions of coumarin and its analogs are generalized. Since coumarin derivatives are characterized by enhanced photochemically activity, special attention is given to the synthesis of photosensitive compounds and materials with intense fluorescence, including the structures capable of changing fluorescence under the action of various factors: solvent, pH of the medium, and interaction with bioorganic substrates. Pathways for design of fluorescent polymethine dyes, fluorescent labels for proteins, fluorescent photochromes, and photoacids for optical data storage with fluorescence read-out are reviewed. The role of isomerization transformations of the new compounds in their sensorial effects is established. [ABSTRACT FROM AUTHOR]

Solar energy has seen 180 years of development since the discovery of the photovoltaic effect, having achieved the most successful commercialization in the energy-harvesting fields. Despite its long history, even the most state-of-the-art photovoltaics remain confined to solid-state devices, limiting spatial and light utilization efficiencies. Herein, a liquid-state photoenergy harvester based on a photoacid (PA), a chemical that releases protons upon light irradiation and recombines with them in the dark through a fully reversible reaction, is demonstrated. Asymmetric light exposure on a PA solution contained in a transparent tube generates a pH gradient (ΔpH = 2) along the exposed and dark regions, which charges the Nernst potential up to 0.7 V across the two electrodes embedded at each end, as if a capacitor. Owing to the reversibility of PAs, a PA-driven liquid-state photoenergy harvester (PLPH) generates capacitive currents up to 0.72 mA m -2  on an irradiation. Notably, the transparent nature of the PLPH enables vertical stacking up to 25 units, which multiplies the light-harvesting efficiencies by over 1000%. This unique approach provides a new route to harness solar energy with a form-factor-free design that maximizes spatial and light-use efficiencies., (© 2022 Wiley-VCH GmbH.)